Reverse link pilot integrated with block codes

ABSTRACT

A method and apparatus for encoding digital communication signals is described herein. A wireless communication unit may comprise a processor configured to produce first symbols derived from data bits and parity bits. The wireless communication unit may transmit a wireless signal including the first symbols and reference symbols in a time interval including a plurality of symbol time intervals. In one of the symbol time intervals a plurality of the reference symbols may be transmitted in a predetermined pattern, which may have the reference symbols not adjacent to each other. A base station may receive a wireless signal including first and reference symbols. In one of the symbol time intervals a plurality of the reference symbols may be received in a predetermined pattern. The base station may then demodulate the first symbols using the reference symbols, wherein the first symbols are derived from data bits and parity bits.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/480,116, filed on Sep. 8, 2014, which is a continuation of U.S.patent application Ser. No. 13/311,151, filed Dec. 5, 2011, which issuedas U.S. Pat. No. 8,830,977 on Sep. 9, 2014, which is a continuation ofU.S. patent application No. Ser. 12/290,755, filed Nov. 3, 2008, whichissued as U.S. Pat. No. 8,072,958 on Dec. 6, 2011, which is acontinuation of U.S. patent application Ser. No. 10/874,101, filed Jun.22, 2004, which issued as U.S. Pat. No. 7,447,187 on Nov. 4, 2008, whichis a continuation of U.S. patent application Ser. No. 09/728,575, filedNov. 30, 2000, which issued as U.S. Pat. No. 6,804,223 on Oct. 12, 2004,the contents of which are all hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to communications systems and inparticular to a scheme for digital encoding of signals in a wirelesssystem.

Demand for wireless communications equipment and services continue togrow at an unprecedented rate throughout the world. Increasingly, suchsystems are commonly relied upon to provide voice and datacommunications to a growing sector of the public. While these systemsoriginally depended upon analog signaling technology, there isessentially unanimous agreement that future systems will be based onvarious types of digital signal coding schemes.

The typical wireless communication system is a point to multi-point typesystem in which a central base station communicates with a number ofremote units located within a local geographic area of coverage known asa cell. This system provides for duplex communication such that signalsmay be sent in both a forward direction (from the base station to theremote unit) as well as in a reverse direction (from the mobile remoteunit back to the base station). In order to support communicationbetween the remote unit and networks such as the Public SwitchedTelephone Network (PSTN), or data networks such as the Internet, thewireless system must also provide for various logical components andfunctional entities.

Consider the Code Division Multiple Access (CDMA) and Time DivisionMultiple Access (TDMA) digital systems presently in widespread use. Eachof these systems provides for certain logical types of the radiochannels that make up the forward link and reverse link. In particular,the forward link channels often include a pilot channel, pagingchannels, and multiple forward traffic channels. The traffic channelsare used to carry the payload data between the base station and themobile unit. A pilot channel is also typically required to allow theremote unit to maintain synchronization with the base station. Thepaging channels provide a mechanism for the base station to inform theremote unit of control information, such as the assignment of forwardtraffic channels to particular connections and/or subscriber units.

Likewise, an access channel is provided in the reverse direction inaddition to reverse traffic channels. The access channels allow theremote units to communicate control information with the base station,such as to send messages indicating the need to allocate or deallocateconnections as required.

Various environmental conditions will affect the performance of anywireless communications system. These elements include atmosphericsignal path loss, which may often introduce fading and interference.Fading may include variations that are introduced as a result of thespecific terrain within the cell, as well as other types of fading, suchas multi-path fading, that occurs due to signal reflections fromspecific features, such as buildings that cause fluctuations in receivesignal strength. Systems in which the remote unit may be a mobile unit,especially those potentially operating at higher speeds, such as thecellular telephones used in automobiles, are particularly susceptible tomulti-path fading. In such an environment, the signal pathways arecontinually changing at a rapid rate.

Certain techniques can be used to attempt to eliminate the detrimentaleffects of signal fading. One common scheme is to employ specialmodulation and/or coding techniques to improve the performance in afading environment. Coding schemes such as block or convolutional codingadd additional parity bits at the transmitter. These coding schemes thusprovide increased performance in noisy and/or fading environments at theexpense of requiring greater bandwidth to send a given amount ofinformation.

In addition, pilot signals may also be used to provide a reference foruse in signal demodulation. For example, most digital wirelesscommunications systems provide for a dedicated pilot channel on theforward link. This permits the remote units to remain in timesynchronization with the base station. Certain systems, such as theIS-95 CDMA system specification promulgated by the TelecommunicationsIndustry Association (TIA) use the pilot signals that includepseudorandom binary sequences. The pilot signals from each base stationin such a system typically use the identical pseudorandom binarysequence, with a unique time offset being assigned to each base station.The offsets provide the ability for the remote stations to identify aparticular base station by determining this phase offset in the forwardlink pilot channel. This in turn permits the remote units to synchronizewith their nearest neighboring base station. Coding the pilot channel inthis way also helps support other features, such as soft handoff forcell-to-cell mobility.

The pilot signal, having a predictable frequency and rate, allows theremote units to determine the radio channel transfer characteristics. Bymaking such determinations, the receiver may in turn further compensatefor the distortion introduced in the channel during the process ofestimating symbols being received.

However, it is generally considered to be impractical to use pilotsignals in the reverse link. In particular, this would lead to asituation where pilot signal channels would have to be dedicated foreach remote unit. While this would not necessarily pose a problem in apoint to point system, in point to multi-point systems such as acellular telephone network, the architecture would quickly lead toinefficiency in use of the available radio spectrum. In addition, it isgenerally thought that the overhead associated with a system thatassigned individual pilot channels to each remote unit wouldunnecessarily complicate the base station receiver processing.

An alternative to allocating individual pilot channels is to make use ofa sequence of pilot symbols. The pilot symbols are interleaved with datasymbols on the traffic channel. This technique is generally referred toas pilot symbol assisted modulation. In such a system, the transmitterencodes the data to be sent on the traffic channel as a series ofsymbols. A pilot symbol interleaver then inserts a sequence ofpredetermined pilot symbols within the data symbol sequence. The pilotsymbol augmented sequence is then modulated and transmitted over theradio channel. At the receiving station, a decimeter or deinterleaverand filter separate the pilot symbols from the data symbols.

SUMMARY OF THE INVENTION

What is needed is a way to integrate pilot symbol assisted modulationtechniques with block encoding schemes in a way which maximizes theprobability that data and pilot symbols will be correctly received.

The invention accomplishes this with a pilot symbol insertion schemethat proceeds as follows. The source data bits are first augmented withperiodically inserted pilot symbols. In a preferred embodiment, thepilot symbols are inserted at a position corresponding to a power oftwo, such as for example, every fourth, eighth, sixteenth, orthirty-second symbol. Next, this pilot symbol augmented data sequence ispresented to a deterministic block coder. Such a block coder may, forexample, be a sub-rate two dimensional turbo product coder.

The symbols of the resulting encoded block are then rearranged such thatthe pilot symbols will be in a predictable location. Because the pilotsymbols are always in a known place in the input block coding matrix,their positions are therefore also known in the output block codingmatrix. The encoded output pilot symbols can therefore be rearrangedsuch that they are evenly distributed through the output coded space,prior to modulation and transmission.

An optional embodiment makes use of an interleaving scheme in whichparity symbols are interleaved with data and pilot symbols. In such ascheme, all symbols from the coded space, with the exception of thepilot symbols, are placed in a temporary storage area by row. Data isthen read out of the temporary storage area to provide the interleavedoutput, by reading data from the temporary array in column order. Forexample, a first pilot signal is selected, a row is read out, a secondpilot signal is selected, a second row is read out, and so on. As aresult, the pilot symbols are output at predetermined positionspreferably located within symbol positions which are a power of two awayfrom each other.

In an alternate embodiment, the symbols may be composed of pairs ofinput data bits, to form complex -valved symbols, which can then bemodulated using Quadrature Phase Shift Keyed (QPSK) schemes. In thisembodiment, the data, parity, and pilot bits are processed in pairs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a communication system which encodes pilotsymbols according to the invention;

FIG. 2 is a more detailed diagram of a transmit encoder and receivedecoder;

FIGS. 3A and 3B illustrate how a deterministic block encoder, such as aone-quarter rate turbo product encoder, distributes data and parity bitsin an output matrix;

FIGS. 3C and 3D illustrate how the pilot inserter and block encoderoperate according to the invention;

FIG. 4A illustrates how a first type of interleaver outputs pilot, data,and parity bits;

FIGS. 4B and 4C illustrate how a second type of interleaver may orderthe data, parity, and pilot bits; and

FIG. 4D illustrates how a third type of interleaver may order data,parity and pilot bits for use with a Quadrature Phase Shift Keyed (QPSK)type modulator.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

FIG. 1 is a block diagram of a communication system 10 that interleavespilot symbols with data symbols and uses a systematic block coder toensure that the pilot symbols are located in predetermined locations. Inthe following description of a preferred embodiment, the communicationsystem 10 is described such that the shared channel resource is awireless or radio channel. However, it should be understood that thetechniques described here may be applied to allow shared access to othertypes of media such as telephone connections, computer networkconnections, cable connections, and other physical media to which accessis granted on a demand driven basis.

The communication system 10 includes a number of Personal Computer (PC)devices 12-1, 12-2, . . . 12-h, . . . 12-l, corresponding SubscriberAccess Units (SAUs) 14-1, 14-2, . . . 14-h, . . . 14-l, and associatedantennas 16-1, 16-2, . . . 16-h, . . . 16-l. Centrally located equipmentincludes a base station antenna 18, and a Base Station Processor (BSP)20. The BSP 20 provides connections to and from an Internet gateway 22,which in turn provides access to a data network such as the Internet 24,and network file server 30 connected to the network 22. The system 10 isa demand access, point to multi-point wireless communication system suchthat the PCs 12 may transmit data to and receive data from networkserver 30 through bi-directional wireless connections implemented overforward links 40 and reverse links 50. It should be understood that in apoint to multi-point multiple access wireless communication system 10 asshown, a given base station processor 20 typically supportscommunication with a number of different subscriber access units 14 in amanner which is similar to a cellular telephone communication network.

The PCs 12 may typically be laptop computers 12-l, handheld units 12-h,Internet-enabled cellular telephones or Personal Digital Assistant(PDA)-type computers. The PCs 12 are each connected to a respective SAU14 through a suitable wired connection such as an Ethernet-typeconnection.

An SAU 14 permits its associated PC 12 to be connected to the networkfile server 30 through the BSP 20, gateway 22 and network 24. In thereverse link direction, that is, for data traffic traveling from the PC12 towards the server 30, the PC 12 provides an Internet Protocol (IP)level packet to the SAU 14. The SAU 14 then encapsulates the wiredframing (i.e., Ethernet framing) with appropriate wireless connectionframing. The appropriately formatted wireless data packet then travelsover one of the radio channels that comprise the reverse link 50 throughthe antennas 16 and 18. At the central base station location, the BSP 20then extracts the radio link framing, reformatting the packet in IP formand forwards it through the Internet gateway 22. The packet is thenrouted through any number and/or any type of TCP/IP networks, such asthe Internet 24, to its ultimate destination, such as the network fileserver 30.

Data may also be transmitted from the network file server 30 to the PCs12 in a forward direction. In this instance, an Internet Protocol (IP)packet originating at the file server 30 travels through the Internet 24through the Internet gateway 22 arriving at the BSP 20. Appropriatewireless protocol framing is then added to the IP packet. The packetthen travels through the antenna 18 and 16 to the intended receiver SAU14. The receiving SAU 14 decodes the wireless packet formatting, andforwards the packet to the intended PC 12 which performs the IP layerprocessing.

A given PC 12 and the file server 30 can therefore be viewed as the endpoints of a duplex connection at the IP level. Once a connection isestablished, a user at the PC 12 may therefore transmit data to andreceive data from the file server 30.

The reverse link 50 actually consists of a number of different types oflogical and/or physical radio channels including an access channel 51,multiple traffic channels 52-1, . . . 52-t, and a maintenance channel53. The reverse link access channel 51 is used by the SAUs 40 to sendmessages to the BSP 20 to request that traffic channels be granted tothem. The assigned traffic channels 52 then carry payload data from theSAU 14 to the BSP 20. It should be understood that a given IP layerconnection may actually have more than one traffic channel 52 assignedto it. In addition, a maintenance channel 53 may carry information suchas synchronization and power control messages to further supporttransmission of information over the reverse link 50.

Similarly, the forward link 40 typically includes a paging channel 41.The paging channel 41 is used by the BSP 20 to not only inform the SAU14 that forward link traffic channels 52 have been allocated to it, butalso to inform the SAU 14 of allocated traffic channels 52 in thereverse link direction. Traffic channels 42-1 . . . 42-t on the forwardlink 40 are then used to carry payload information from the BSP 20 tothe SAUs 14. Additionally, maintenance channels carry synchronizationand power control information on the forward link 40 from the basestation processor 20 to the SAUs 14.

In the preferred embodiment, the logical channels 41-43 and 51-53 aredefined by assigning each channel a unique pseudorandom channel (PN)code. The system 10 is therefore a so-called Code Division MultipleAccess (CDMA) system in which channels assigned to unique codes may usethe same radio carrier frequency. The channel may also be furtherdivided or assigned. Additional information as to one possible way toimplement the various channels 41, 42, 43, 51, 52, and 53 is provided inPatent Cooperation Treaty Application No. WO 99/63682 entitled “FastAcquisition Of Traffic Channels For A Highly Variable Data Rate,”assigned to Tantivy Communications, Inc., and published Dec. 9, 1999. Ina preferred embodiment, the channel codes are a type of PN code whichrepeats at a code length of 2^(N). One such orthogonal PN code scheme isdescribed in U.S. patent application Ser. No. 09/255,156, filed Feb. 23,1999, entitled “Method and Apparatus for Creating Non-InterferingSignals Using Non-Orthogonal Techniques”, assigned to TantivyCommunications, Inc.

Turning attention now to FIG. 2 there is shown a generalized blockdiagram of the encoding process at the transmit side and decodingprocess at the receive side according to the invention. It should beunderstood that the invention is implemented on the reverse link 50, sothat the transmitter 100 may typically be one of the SAUs 14 and thereceiver is the Base Station Processor (BSP) 20. However, in otherimplementations it is possible for the invention to be applied on theforward link 40, in which case the transmitter is implemented in the BSP20 and the receivers is the SAUs 14.

In any event, a transmitter 100 is implemented with a pilot inserter110, block encoder 120, pilot interleaver 130, channel coder 140 andradio frequency (RF) modulator 150. The receiver 200 includes an RFdemodulator 250, channel decoder 240, pilot deinterleaver 230, blockdecoder 220, pilot removal 210, and pilot reference generator 205.

It should be understood that the receiver 200 performs the inversefunctions of the corresponding portions of the transmitter 100. In suchan instance, the RF demodulator 250 performs the inverse radio frequencyto modulation process, the channel decoder 240 decodes the channel codesreversing the operation of the channel coder 140, the pilotdeinterleaver 230 performs the inverse function of the specific pilotinterleaver 130 implemented in the transmitter, and the block decodeprocess 220 also undoes the block encode process 120. The pilot removalprocess 210 uses a pilot reference signal generator 205, for example, tomultiply the received data in pilot stream via reference pilot signal tofurther aid in the recovery of the data. A pilot inserter 110 typicallymakes sense in the reverse link 50 given and that pilot symbols arepreferably inserted with the data symbols or bits in this same channel.This is opposed to an arrangement where there are separate pilotchannels devoted separately for simply sending pilot signals, which istypically more practical on the forward link 40, in which case a singlepilot channel can be associated with and be shared by numerous SAUs 14.

Before discussing the details of the pilot inserter 110 and blockencoder 120 in more detail, it is instructed to consider the operationof a typical error coding process. In particular, consider an examplesituation in the use of a turbo product code which is to encode data atthe rate of ¼. (We assume in the discussion of this first embodimentthat data is real-valued only such that a “symbol” is a single data bit,and discuss a situation with complex-valued data symbols later on.) Inthe case shown in FIG. 3A, the input data bits data 1, data2 . . .data16 may thought of as being placed in the upper left hand corner of amatrix encoding space. Because the code is a ¼ rate code, the matrixencoding space consists of a matrix which is four times the size of theinput data matrix space. In the current example the input data matrixspace is 4×4, and the coded space is a matrix of 8×8.

For a typical prior art block coding operation, that is one withoutsupplementation with pilot symbols according to the invention, the 16input data bits are placed in an upper left hand corner of the 8×8encoded space as shown in FIG. 3A.

The encoded matrix is then presented to the block encoder to calculateand create the parity bits for an encoded space. In the example beingdiscussed, in the case of a ¼ rate code, three times as many parity bitsas data bits are calculated and created as shown in FIG. 3B. This typeof systematic turbo product code, is considered to be deterministic inthe sense that input data bits appear in the same position in the outputmatrix as they do in the input matrix, with all of the parity bitstaking up the other spaces in the matrix.

Returning attention to FIG. 2, the pilot inserter 110 and block encoder120 can now be understood more particularly. In the pilot insertionscheme employed by the pilot inserter 110, some of the input datasymbols are replaced with pilot symbols. In the preferred embodiment,the goal is to have pilot symbols make up approximately 6.25% of thedata symbols sent on the channel after encoding. That means for every 64channel symbols there needs to be 4 pilot symbols inserted into theinformation space.

Turning attention to FIG. 3C, we see that in considering a group of 16data symbols, 4 of the symbols will be replaced with pilot symbols suchthat the input matrix becomes as shown. Thus a pilot symbol, pilot1, isfollowed by three data symbols, data1, data2, data3. The next pilotsymbol, pilot2, is followed by data symbols data4, data5, data6 and soon.

As in the case of the standard turbo product code, the matrix in FIG. 3Cis then presented to the block encoder 120 to create the encoded spaceshown in FIG. 3D. The parity symbols of this example will, in fact, bedifferent from those for the situation where the non-insertedinformation space because the information space has changed between thetwo examples. In particular, of course, the information space in FIG. 3Cis different from the information space in FIG. 3A, and so the paritysymbols parity₁, parity₂ . . . parity₄₈ are different. What is importantto note here is that the pilot symbols pilot₁, pilot₂, pilot₃ and pilot₄are still in the same identifiable positions in the matrix.

It is the job of the pilot interleaver 130 to rearrange the outputmatrix in such a manner that the pilot symbols are evenly distributedamong the data and parity symbols in a manner which makes sense. In thesimplest instance, the data and parity symbols can be placed on thechannel in, more or less, the order in which they appear in the matrix.This situation is shown in FIG. 4A. In particular, it is noted that thepilot symbols pilot1, pilot2, pilot3 are redistributed through thematrix so that they are read out once every 16 bits, or 6.25% of thetime, as desired. The matrix can thus be interpreted as a set ofinstructions for ordering the output bits, by reading along the firstrow, and then reading the bits out along the second row, and then alsothe third row, and so on.

In certain other instances it is important to interleave the paritysymbols among the pilot and data symbols as well. In this situation, theparity symbols and data symbols can be better distributed throughout theinformation space. In this approach, all except the pilot symbols may beplaced in a temporary storage area 180 in row order fashion and thenread out by column order. The goal in allocating rows and columns in thetemporary storage area 180 is to remain as square as possible. Thus, inthe example illustrated shown in FIG. 4B, the data and parity symbolsare first read out from a first row of the coded output matrix in FIG.4A, while saving the pilot symbols in another temporary storage area.The result is a matrix having the data1, data2, data3, parity1, parity2,parity3 . . . parity47, parity48 symbol arrangement as shown. Data isthen read out of this temporary storage area 180 by reading out thenon-pilot symbols in column order. Thus, for example, as shown in FIG.4C, a first pilot symbol is read out of the pilot matrix, and thenfifteen symbols are read from the non-pilot storage area (data1,parity4, parity7, parity10, and so on) resulting in the order of symbolsshown in the first row of FIG. 4C. This results not only in the pilotsymbols continuing to be distributed once every 16 symbols, but also ina situation such that the data symbols are more evenly disbursedthroughout the encoded space.

In yet another example of the implementation of the interleaver 130, itmay be advantageous to apply data to the channel with Quadrature PhaseShift Keyed (QPSK) format modulation. In this case, individual inputdata bits are read in pairs so that for example, 2 pilot bits arerequired to make up respectively the In-phase (I) and the Quadrature (Q)portion of a complex valued data symbol. In this case, pilot bits arealso read out in pairs so that two pilot bits comprise a pilot symbol.The result, as shown in FIG. 4D, is a situation in which pilot symbols(consisting of a pilot₁ and pilot₂ bit) still appear every 16 symbols or6.25% of the time.

Using the systematic block encoder, the position of the pilot,information, and parity symbols is always known in the output matrix.This creates a structure where pilot symbols can be repositioned in aknown fashion, to ensure that they repeat in a regular pattern in themodulated output signal.

For example, a system timing requirement may demand that the ratio ofpilot symbols to the ratio of data and parity symbols remain at a powerof two, so that clock phasing requirements are much easier to meet. Inparticular, even if a block encoder produces a number of data and paritysymbols as a power of 2, the additional pilot symbol insertions wouldcreate an output sequence which is not an exact power of 2. This makesit difficult to insert pilot symbols in blocks which do not remain inphase, and therefore “roll” with respect to the PN sequences used withrespective channel encoding 140. For example, in a case where pilotsymbols need to be inserted 6.25% of the time, a block of 4096 wouldrequire 4096 for data and parity, plus 6% of 4096, or 256 symbols forpilots for a total of 4352 symbols per block. Because no PN channel codeis such a length, to maintain synchronization, the position of the PNcode would change at the start of every symbol block. However, with theinvention, this difficulty is avoided, and the output symbol blocks areeasily contrived to be in groups of 2N, including both parity and pilotsymbols. Thus, PN code synchronization timing, as required to maintainthe proper spread spectrum characteristics, is easy.

What is claimed is:
 1. A wireless communication unit comprising: aprocessor configured to produce first symbols derived from data bits andparity bits; and a transmitter configured to transmit a wireless signalincluding the first symbols and reference symbols in a time intervalincluding a plurality of symbol time intervals, wherein in one of thesymbol time intervals a plurality of the reference symbols aretransmitted in a predetermined pattern, wherein the predeterminedpattern has the reference symbols not adjacent to each other.
 2. Thewireless communication unit of claim 1, wherein the predeterminedpattern has the reference symbols with a single space separating thereference symbols.
 3. The wireless communication unit of claim 1,wherein the reference symbols are pilot symbols.
 4. The wirelesscommunication unit of claim 1, wherein the first symbols are quadraturemodulated.
 5. The wireless communication unit of claim 1, wherein thefirst symbols are produced by turbo coding the data bits.
 6. A methodfor use in a wireless communication unit, the method comprising:producing first symbols derived from data bits and parity bits; andtransmitting a wireless signal including the first symbols and referencesymbols in a time interval including a plurality of symbol timeintervals, wherein in one of the symbol time intervals a plurality ofthe reference symbols are transmitted in a predetermined pattern,wherein the predetermined pattern has the reference symbols not adjacentto each other.
 7. The method of claim 6, wherein the predeterminedpattern has the reference symbols with a single space separating thereference symbols.
 8. The method of claim 6, wherein the referencesymbols are pilot symbols.
 9. The method of claim 6, wherein the firstsymbols are quadrature modulated.
 10. The method of claim 6, wherein thefirst symbols are produced by turbo coding the data bits.
 11. A basestation comprising: a receiver configured to receive a wireless signal,wherein the wireless signal includes first and reference symbols in atime interval including a plurality of symbol time intervals, wherein inone of the symbol time intervals a plurality of the reference symbolsare received in a predetermined pattern, wherein the predeterminedpattern has the reference symbols not adjacent to each other; and aprocessor configured to demodulate the first symbols using the referencesymbols, wherein the first symbols are derived from data bits and paritybits.
 12. The base station of claim 11, wherein the predeterminedpattern has the reference symbols with a single space separating thereference symbols.
 13. The base station of claim 11, wherein thereference symbols are pilot symbols.
 14. The base station of claim 11,wherein the first symbols are quadrature modulated.
 15. The base stationof claim 11, wherein the first symbols are produced by turbo coding thedata bits.